4.2.4. Chloride Attack

Chlorides from de-icing salts or seawater cause reinforcement corrosion.

Chloride attack refers to the damaging effect of chlorides on concrete structures, particularly affecting the reinforcement bars inside the concrete. When these chlorides penetrate the concrete due to water exposure or de-icing salts that are commonly used in colder climates, they can reach the steel rebars. This initiates corrosion, leading to the deterioration of the steel and ultimately weakening the concrete structure.

Imagine a steel spoon left in water for a long time; over time, rust will form due to the exposure to moisture and salt. Similarly, in concrete, chlorides act like the water that leads to rusting of the steel rebar, causing long-term damage to the entire structure.

Chlorides may originate from environmental sources such as seawater or from the application of de-icing salts on roads during winter.

Chlorides can enter the concrete mix in two main ways: through seawater, which is highly saline, and through de-icing salts commonly used on roads during winter. Both sources are prevalent, especially in coastal and cold regions, respectively. When concrete is placed in these environments, it becomes susceptible to chloride ion ingress, leading to potential corrosion issues.

Think of how saltwater can corrode a metal boat left in the ocean. In the same way, when concrete structures are exposed to seawater or de-icing salts, they face a similar risk of damage over time.

Corrosion of reinforcement leads to expansion, cracking, and eventual spalling of concrete, compromising structural integrity.

When the steel reinforcement inside concrete starts to corrode due to chloride exposure, it begins to expand. This expansion creates internal stresses in the surrounding concrete, leading to cracks and spalling (the flaking or chipping off of the concrete surface). As a result, the structural integrity of the concrete is compromised, which may lead to serious safety concerns, including structural failure if not addressed.

Consider a balloon being inflated. As more air (or in this case, rust) accumulates inside the balloon (the concrete), it stretches and may eventually pop (spall). This demonstrates how internal pressures from corrosion can adversely affect the concrete structure around it.

Use pozzolans, epoxy-coated bars, and surface sealers to mitigate chloride attack.

To prevent chloride attack from compromising concrete, several strategies can be employed. Using pozzolans such as silica fume or fly ash in the concrete mix can help reduce permeability, making it less susceptible to chloride ingress. Additionally, using epoxy-coated reinforcement bars provides a protective layer that prevents chlorides from reaching the steel. Surface sealers can also be applied to the concrete's exterior, creating a barrier against water and chloride penetration.

Think of wearing a raincoat on a rainy day. The raincoat protects you from getting wet, much like how epoxy coatings and sealers protect concrete from chlorides. This proactive approach helps keep our concrete structures safe from chloride-induced corrosion.

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